Federal Reserve Chairman Ben S. Bernanke said central banks around the world will probably unwind monetary expansion policies at different times because of differences among their economies.

“In the medium term, like the Federal Reserve and many other central banks, the Bank of Korea will have to manage its exit from accommodative policies,” Bernanke said in pre-recorded remarks to a participants in a conference hosted by South Korea’s central bank in Seoul yesterday.

The Bank of Korea “will have to weigh the risks of a premature exit against those of leaving expansionary policies in place for too long,” Bernanke said.

Bernanke praised South Korea’s response to the global financial crisis over the last few years, including its decisions to reduce its policy interest rate by 3.25 percentage points and to set up a fund to keep its banking system stable.

In the US, the Fed cut its benchmark interest rate to near zero in December 2008 and purchased $1.7 trillion in Treasuries and housing debt to revive growth.

Officials are debating when and how fast to raise rates and sell mortgage assets.

“Because economic conditions vary, the appropriate timing of the exit is likely to differ across countries,” Bernanke said.

Countries must cooperate to improve financial regulation and ensure that firms are “well capitalized, liquid and transparent,” Bernanke said. The leadership of the Group of 20 countries is “essential,” Bernanke said.